What does it measure?
Creatinine is a waste product of normal muscle metabolism. The kidneys remove it from the blood. Laboratories commonly use blood creatinine, age, and sex in an equation to estimate glomerular filtration rate, or eGFR, which gives more useful context than creatinine alone. [1]
Before the test
- Sample
- A blood sample from a vein.
- Preparation
- Follow the laboratory’s meal instructions and mention creatine supplements, recent hard exercise, and medicines.
What can the result mean?
Higher creatinine can indicate reduced filtration, but dehydration, substantial muscle mass, recent meat intake, strenuous exercise, or some medicines can contribute. Low creatinine may reflect lower muscle mass rather than especially strong kidney function. A change from your own previous result can be important even within the laboratory interval. [1]
When is it useful, and how is it read?
An increase from your previous result can matter even before a laboratory flag appears. Clinicians compare the trend, eGFR, urine findings, and the circumstances of the change. When muscle mass makes creatinine misleading or a decision needs greater precision, cystatin C may improve the filtration estimate. [1] [2] [5]
Reading the results together
| Marker | What it adds |
|---|---|
| Creatinine | A measured waste product influenced by muscle and kidney clearance. |
| eGFR | An estimate of filtration using blood markers and personal inputs. |
| Microalbuminuria, Random Urine (Alb-Creat Ratio) | A separate view of albumin leakage in urine. |
A creatinine result makes more sense alongside its filtration estimate, urine findings, and previous results. Each adds a different part of the kidney picture. [1] [3] [4]
What can affect it?
Mention creatine supplements, training, recent illness, and all medicines. Some medicines change creatinine handling without the same change in filtration. In people with unusually high or low muscle mass, a cystatin C-based assessment may help clarify kidney function. [1]
Low creatinine can reflect less muscle
Creatinine production depends partly on muscle mass. A low concentration can therefore reflect a smaller muscle pool, rather than exceptionally strong kidney filtration; the same number can have different meaning in different people. [5] [6]
Questions you might have
Can a meat meal affect creatinine?
Yes. Meat can temporarily raise it. Follow the laboratory’s preparation instructions so repeat results are easier to compare. [1]
Why is eGFR reported beside creatinine?
eGFR uses creatinine and other information to estimate kidney filtration. Creatinine alone also depends on muscle and other factors. [3]
What comes next?
Read the result with eGFR, urine albumin-to-creatinine ratio, blood pressure, and previous values. Your clinician can decide whether repeat testing is needed and how soon. A rapid rise or markedly reduced urine output needs prompt assessment; it should not be assumed to be a routine variation. [1]
Could muscle, supplements, or medicines affect this result, and would cystatin C help?
The reference interval and units on your report are part of understanding your result. Understand units, reference intervals, and treatment targets.
Sources & references
Medical references & original research
- MedlinePlus — Creatinine Test
- NIDDK — Glomerular Filtration Rate Equations
- NIDDK — Chronic Kidney Disease Tests & Diagnosis
- NIDDK — Estimated Glomerular Filtration Rate Calculators
Books we consulted
References that informed our explanations of the test and its context.
- Pagana KD, Pagana TJ, Pagana TN. Mosby’s Diagnostic and Laboratory Test Reference. 14th ed. Elsevier; 2019.
- Moisio MA, Moisio EW. Understanding Laboratory and Diagnostic Tests. Delmar Publishers; 1998.
Practical-section sources accessed: .
For general health education. Interpreting your result and deciding on tests or treatment requires your health context and a qualified clinician.
